Independent of colour, this differs from _R. Tucanus_ in having the bill less curved, the top convex and obscure pink, not flat and blue. The belt at the base is always vivid blue (grey in the dead bird), not, as in _R. Tucanus_, of a rich yellow. This I have never met with in Brazil; the other is common from lat. 8 to 23deg S. A drawing from the live bird by the late Sydenham Edwards (obligingly lent me by Lord Stanley) confirms others I have seen as to the colour of the bill, orbits, &c. It varies, however, in that of the throat, breadth of the red band, and in the tail-covers. A specimen I possess being somewhat larger, the breast is nearly white, and the upper tail-covers sulphur. In young birds the white on the sides is tinged with grey. I am inclined to consider the _Grand Toucan a ventre rouge_ of Vaillant as a mere variety, having the red pectoral bar very broad. In general size it is rather larger than the Brazilian Toucan. Our figure is on the exact scale of four-tenths to an inch. Its precise locality I am unacquainted with. We hope to enlarge more on this interesting genus in another publication. * * * * * Pl. 57 [Illustration] UNIO nasutus. _Rostrated River-Mussel._ * * * * * GENERIC CHARACTER. _Testa transversa, aequivalvis, non affixa; natibus decorticatis, suberosis; impressio muscularis postica composita. Dens cardinalis unicus, brevis, irregularis, simplex aut bipartitus, substriatus; dentes laterales duo, elongati, compressi, infra pubem producti._ Typus Genericus _Mya Pictorum_. Linn. Shell transverse, equivalve, not affixed, the tops decorticated. Posterior muscular depressions double. Cardinal tooth one, short, irregular, simple or double, striated; lateral teeth two, elongated, compressed, and prolonged beneath the corslet. Generic Type _Mya Pictorum_. Linn. * * * * * SPECIFIC CHARACTER. _U. (Div. 2.) testa transversim elongata, margine dorsi recta, antice angulata oblique attenuata, extremitate subtruncata._ Unio (Div. 2.). Shell transversely elongated: dorsal margin straight; anterior side angulated, obliquely attenuated, the extremity slightly truncated. _Lister, tab._ 151. _fig._ 6. Unio nasutus. _Say in Encycl. Am. Conch. pl._ iv. _fig._ 1. * * * * * This is one of the most natural genera in the modern systems of conchology, as it includes all fresh-water bivalves having two rough cardinal teeth in one valve and one in the other. The colours of all are more or less dark-brown, sometimes radiated with green; but the specific characters rest on the contour of the shell and the proportion of the teeth.